The Philadelphia Zoo was the first zoo open to the public. It is very, very clean and the animals appear to be well cared for. In addition the animals are located in specially designed habitats. The staff are extremely friendly and helpful and are more than willing to answer your questions. Admission prices are reasonable. Also, for another $10/$12 you can ride the Zooballoon, which I believe goes up to about 400 feet, and enjoy the great views of Fairmount Park and the rest of the city.
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